Various boron compounds have recently been attracting attention as light-emitting materials, electron-transport materials, electron-injection materials, and hole-blocking materials for use in organic light-emitting diode (OLED) devices, or organic semiconductor materials for use in organic thin-film transistors. For example, Japanese Patent Laid-Open Publication No. 2006-96934 discloses a boron compound which has three aromatic groups or heterocyclic groups and which forms a complex with an amine compound or a phosphine compound. Japanese Patent Laid-Open Publication No. 2007-70282 discloses a triaryl boron derivative which has three aryl groups to each of which a heteroaryl group is bonded through an arylene group. Japanese Patent Laid-Open Publication No. 2007-77033 discloses a triaryl boron compound which has three aryl groups including one to which a triazine group having two carbazole groups is bonded. International Publication WO 2005/062675 discloses a triaryl boron compound which has three aromatic carbocyclic groups or heterocyclic groups. These boron compounds are all triaryl boron compounds in which three aryl groups or heteroaryl groups are bonded to a boron atom. In the past, most boron compounds have been limited to those having such a bonding pattern.
In contrast, coordination compounds of boron have been studied. For example, Japanese Patent Laid-Open Publication No. 2007-35791 discloses a boron compound in which the fourth group is coordinated to a boron atom having three substituent groups. International Publication WO 2005/062676 discloses a boron compound in which the fourth group is coordinated to a boron atom having two substituent groups and one aromatic carbocyclic group or heterocyclic group. Angew. Chem. Int. Ed. 2006, 45, 3170-3173 discloses a boron compound in which a thienylthiazole group is bonded to a boron atom having two aryl groups, and further, the nitrogen atom of the thiazole ring is coordinated to the boron atom. These boron compounds are a new group of compounds which utilize the electron acceptability of boron, and are extremely interesting. In particular, Angew. Chem. Int. Ed. 2006, 45, 3170-3173 describes that the boron compound disclosed therein may be preferred as an electronic material, because the nitrogen atom of the thiazole ring is coordinated to the boron atom, and therefore, the lowest unoccupied molecular orbital (LUMO) is lowered. However, from the viewpoint that three aryl groups or heteroaryl groups are bonded to a boron atom, all these boron compounds fall into the same category as that of the triaryl boron compounds disclosed in Japanese Patent Laid-Open Publications Nos. 2006-96934, 2007-70282, and 2007-77033, and International Publication WO 2005/062675.